1. Field of the Invention
The present invention relates to an electromagnetic coupling device, for example, to be used for feeding a set of papers in a copying machine.
2. Description of the Prior Art
Heretofore, there has been proposed, for example, an electromagnetic coupling device as disclosed in Japanese Utility Model Examined Publication No. Sho 63 (1988)-29949 having a construction as shown in FIG. 1 of the accompanying drawings with an intention to improve the devices as shown by FIG. 2 of this application, the same as FIG. 4 of the above-mentioned Utility Model Examined Publication No. Sho 63 (1988)-29949, which corresponding to U.S. Pat. No. 4,664,238 shown as one of the prior arts aimed to be improved on. The electromagnetic device as shown by the above-mentioned FIG. 2 is constructed in a manner as explained below.
Referring now to FIG. 2, numeral 1 denotes a stator as a yoke which receives therein a coil 2 and is fixedly engaged with a stationary member (not shown).
Numeral 3 is a rotor as one of a coupling member being fixedly attached with a lining 4 and is forcibly fitted around the outer periphery of a hollow rotary shaft 5 fabricated of an iron series magnetic material.
Numeral 6 designates a hub generally formed as a cylindrical member by plastic molding or by sintering alloy powders and the outer periphery of which is provided with a gear and is directly fitted around the outer periphery of said rotary shaft 5 so as to be permitted for relative slidable rotation.
Numeral 8 is a return leaf spring attached to the hub 6 and the portion which faces the said lining 4 is attached with an armature 9, as the other coupling member by means of a rivet 10.
A predetermined extent of gap g is maintained between the armature 9 and the rotor 3. Numeral 11 is a metal of an iron series alloy inserted between the stator 1 and the rotary shaft 5, 12 a spacer, 13 and 14 are retaining rings fitted around the rotary shaft 5 for positioning the stator 1, rotor 3 and the hub 6 in axial direction.
Numeral 15 in the drawing denotes a set screw for fixing the electromagnetic clutch to a driven shaft 16, which is normally inserted, at the operation site of the user, into the central opening of the hollow rotary shaft of the coupling device assembled and shipped from the manufacturer without placing such a driven shaft.
The electromagnetic coupling device or clutch of modified construction shown in FIG. 1 is constructed in a manner as explained below.
In FIG. 1, the same reference numerals are placed to the parts or components which are substantially the same as or similar to those shown in FIG. 2 and the detailed explanation thereof are omitted.
In FIG. 1, numeral 17 denotes a rotor which differs from the rotor 3 shown in FIG. 2 with respect to its feature that its magnetic pole 18 is formed such that a magnetic flux .PHI. directly flows through an air gap g.sub.1. Numeral 19 denotes a rotary shaft fabricated of a nonmagnetic oil impregnated plastics by molding technique, to which above-mentioned stator 1 and hub 6 are slidably attached.
The outer peripheral surface of the rotary shaft 19 is integrally formed with stepped portions 20 and a groove 21, respectively, as a fixing portion or portions and a straight ridge portion 22 as a fixing portion for positioning the rotor 17 in a circumferential direction.
In addition, the inner surface of the rotary shaft 19 is integrally formed with a fitting face 19a to be fitted onto the so-called D-cut face 23 of the driven shaft 16 so that the rotary shaft 19 will never rotate relative to the driven shaft 16.
Numeral 24 is a retaining ring to be fitted into the above-mentioned groove 21 for positioning the hub 6 in an axial direction.
The modified conventional electromagnetic clutch shown in FIG. 1 and explained above, however, still has several drawbacks as mentioned below.
(1) The rotor 17 can be secured, by virtue of the straight ridge portion 22, with respect to the rotary shaft 19 in the direction of rotation, so that these two members always rotate integrally. However, since they are fixed through the aforesaid straight ridge in axial direction, when the rotor 17 shifts toward the other coupling members 6 and 9, it is liable to be accompanied by an undesired rotation of the rotary shaft 19 following the rotation of the rotor 17.
(2) If the length of the magnetic pole 18 of the rotor 17 is reduced, the rotor 17 would become unstable, since the rotor 17 is liable to incline.
In addition, due to the fact that it necessitates magnetic pole 18, the cost for making the rotor 17 become inevitably expensive.
(3) Two retaining rings 24 and 24' shown in FIG. 1 bring about lengthy man hours in setting work and high production cost.
In other words, both the retaining ring 24 for preventing the hub 6 from escaping from the rotary shaft and the other retaining ring 24' for preventing the rotary shaft 19 from its slipping out from the driven shaft 16, are indispensable, and these two members are liable to increase the production cost as explained above, and
(4) Since the rotary shaft 19 and the rotor 17 are mechanically joined together, there is no such serious problems as in the above items (1) and (2), but the rotary shaft 19 made of magnetic soft iron results in high production cost.